1. Field of the Invention
The present invention relates to an image processing apparatus capable of correcting density by using a reusable object, a control method for such an image processing apparatus, and a storage medium. The reusable object is a repetitive object which can be referenced a plurality of times and is used in variable data printing (VDP).
2. Description of the Related Art
In recent years, according to the expansion of one-to-one marketing, direct mails, which are useful in providing needs-matched information to customers, are becoming popular. Direct mails contain data such as variable data. A special page description language for VDP, typified by Personalized Print Markup Language (PPML), is used when variable data of a direct mail is printed.
The VDP data includes three elements: a reusable object, a number of variable objects, and page description language. The reusable object is repeatedly used in a plurality of pages. The variable object includes information which can be changed page by page such as customer information. The page description language defines the nature of the document information. The reusable data in this context denotes the repetitive object.
Further, regarding presentation application such as Microsoft PowerPoint, the same background object is repeatedly used in a number of pages. Normally, since a background object, which is common to all the pages, needs to be repeatedly processed, processing before printing takes time. Under such circumstances, a controller that enables high-speed printing has been developed and is on the market. When a background including the same object is repeatedly used, this controller processes the background image, stores the obtained result, and uses the stored processing-completed object each time the object is used. The background object denotes the repetitive object.
Nowadays, electrophotography is a widely-used method for printing. Since density stability of electrophotography is unstable compared to printing using ink, a technique that allows correction of density by preparing data other than print data, and measuring the change in the prepared data during printing has been developed.
For example, Japanese Patent Application Laid-Open No. 2006-293129 discusses a technique for determining and controlling execution of correction operations related to image forming conditions of an image forming apparatus. According to this technique, the same image is periodically formed and output on print paper. Then, a detected reference image and an image-formed state of the same image are compared. Based on the comparison result, the correction operation is performed. This technique reduces the density variation by correcting the density at regular intervals. Further, Japanese Patent Application Laid-Open No. 2003-195584 discusses a technique that enables simple measurement of an image, not yet completed, on the intermediate transfer member so as to reduce the density variation.
However, according to the technique discussed in Japanese Patent Application Laid-Open No. 2006-293129, since the image for density correction needs to be printed, extra print paper for correcting the density, which is irrelevant to the print job, becomes necessary.
Further, according to the above-described Japanese Patent Application Laid-Open No. 2003-195584, the density variation is measured during the print job. Since image forming needs to be performed while the job is performed, extra toner will be used. Furthermore, according to the method discussed in Japanese Patent Application Laid-Open No. 2003-195584, since the density variation is determined not by the image printed on paper but by the intermediate transfer member, the measurement accuracy is reduced compared to when the density is measured on paper.